Cities of all sizes in the United States employ sewer and other liquid carrying systems for transporting liquid wastes to treatment plants for the disposal thereof. The infrastructure for carrying liquid wastes includes a vast network of underground pipes. The underground pipes can be constructed of many types of material, including clay, metal, cement, plastic, etc. Irrespective of the type of material from which the pipe network is constructed, the pipes deteriorate over time and thus need replacement. Certain pipes can last over 100 years, while other types of pipes may last only 25 years or so.
One technique for replacing old and deteriorated underground pipes includes excavating an open trench to expose the pipe line, and then replacing the old pipes with new pipes. While this technique has been employed for years, it is time consuming, labor intensive and frequently disrupts traffic, if a street or alley requires excavation in order to expose the underlying pipes. Moreover, the street or alley cannot often be immediately repaired until the newly filled trench has settled or otherwise is in condition for the pouring of concrete or laying of asphalt over the trenched area.
Misaligned joints of old underground pipes, cracked pipe sections, and either a complete or partial collapse of the pipe line, are all conditions that frequently exist in municipal wastewater systems. Utility owners are increasingly searching for alternatives to traditional open-cut replacement methods for such failing infrastructure.
Existing pipe lines often have horizontal and/or vertical bends or curves, resulting from dropped joints and/or dramatic elevation changes that can disrupt pipe replacement methods. When a video camera is able to penetrate the existing pipe line to determine that the path is irregular and no longer linear, the best option has been to dig a work pit at the grade or line change location. When the camera is not able to penetrate the old pipe line because of its highly irregular path, the options have been limited to making point repairs prior to using existing trenchless methods, or to revert to traditional open cut methods.
As a significant improvement to the traditional pipe replacement techniques, improved trenchless pipe replacement techniques are disclosed in U.S. Pat. Nos. 5,482,404; 5,816,745 and 6,588,983, the disclosures of which are incorporated herein by reference. This methodology uses the technique of pushing new replacement pipes 24 behind a cone expander 18, through the old pipe line 10 that is being replaced. The trenchless pipe replacing apparatus is shown in FIG. 1, being pushed through an old pipe line 10 toward a manhole 12. The old pipe line 10 is shown curved and irregular, as is the case with many old pipe lines. Pipe replacement is accomplished without using percussion or vibration, and there are no rotating parts. In order to guide the new pipe 24 through the old pipe 10, a multi-component lead train is employed. The lead train includes a lead section 14 that “noses” its way through the path of the old deteriorated pipe 10. A cracker lead 16 functions as a guide behind the lead section 14. There may be a cracker extension (not shown) that effectively extends the length of the cracker lead 16. The cracker lead 16 begins and straightens the path of the old underground pipe 10. Coupled behind the cracker lead 16 is a cracker/cone 18. The leading or frontal portion of this section 18 is fitted with fins 20 placed radially and in a staggered manner. The rear half of the cracker/cone 18 is a concentric cone that fractures the old pipe 10 and expands it radially outwardly into the surrounding dirt. A trailing sleeve 22 is attached to the back of the cracker/cone 18 and makes the two components 18 and 22 rigid with each another as a unit. This rigidity precludes the assembly from reacting to and following every “wiggle” in the old pipe line 10. As shown in FIG. 1 the rigid lead train may exit the irregular path of the old pipe 10 and form a burrow outside the old pipe 10. Should this occur, the pipe replacement operation must be halted due to failure to replace the old pipe.
The rear of the trailing sleeve 22 is fitted with a specific adapter to interface with the new pipe 24 being pushed into the old pipe 10. There can be a lubricant port on the trailing end of the trailing sleeve 22. While not shown, a jacking frame, including a heavy duty hydraulic jack, is employed to exert a force on the back of the new pipe 24, and force it, and the lead train, into the old pipe 10. Once a section of the new pipe 24 has been fully inserted into and in replacement of the old pipe 10, the plunger or cylinder of the jack is retracted and another new pipe section is fitted behind the previously inserted new pipe 24, and the jack pushes the second new pipe section forward, thus pushing the previous pipe and the lead train to advance the apparatus through the path of the old pipe 10. This continues until the front-most new pipe 24 emerges through the old pipe 10 in a downstream manhole 12, whereupon the old pipe line 10 has been completely replaced with new pipe sections.
During the time when the jack is pushing the lead train forward, the fins 20 attached around the cracker/cone 18 rip and break the old pipe 10 as well as any repair clamps or saddles. These fins 20 have been found to point load and break concrete encasement where the concrete is not substantial or is not reinforced. For most pipe replacement conditions, the appropriate cone expander 18 will be concentric, however when certain existing conditions dictate, an eccentric cone expander (not shown) can be used. An eccentric cone expander is used whenever it is expected that the radial expansion of the cone as it moves forward will not expand downward uniformly in all radial directions, i.e. due to an existing rock floor at the bottom of the trench.
In some cases a front jack will be used instead of the trailing sleeve 22. In this case, both a front and rear jack will be employed. It should be noted that with the front jack (a single acting hydraulic cylinder), the frontal components of the lead train can be advanced without advancing the new pipe column. Because of the superior column loading capability of rigid pipe products that are currently available, the front jack is used only when substantially upsizing of the new pipe is desired, as compared to the old pipe, or when the push is long, or the existing ground condition is a hard consolidated material. Whenever the front jack is used there is a pipe adapter which provides a mating surface that allows the front jack to interface with the new pipe column. The lubricant port on the trailing end of the trailing sleeve allows the introduction of lubricant. The lubricant can be of any type, but preferably bentonite, a polymer, or a mixture of both. By introducing a lubricant around the annular space of the new pipe column, the force necessary to advance the column is maintained at a minimum.
The foregoing technique functions very well for many old pipe lines, even pipe lines with gentle or gradual curves. In this event, the gently curbed pipe line may even be straightened due to the rigidity of the coupling between the components of the lead train.
When the lead train components of the pipe train of FIG. 1 are joined together, a rigid assembly is formed. This rigid train of components can be about nine to twelve feet long, and because of its length and rigidity, it cannot navigate the “wiggles” that may exist in many old pipe lines. Stated another way, this rigid assembly will follow the general path of the old pipe line, however it will not follow every misaligned joint. The problem is exacerbated when the old pipe line is situated in soft soil or in sandy conditions. In old pipe lines where misalignment of pipe sections exists, or where the old pipe line is characterized by a curved or meandering path, the path must first be straightened and any misalignment corrected in order to accommodate the new rigid pipe that replaces the old pipe line.
From the foregoing, it can be seen that a need exists for a new trenchless technique, and apparatus, for replacing old pipe lines characterized by irregular paths. Another need exists for a lead train that can follow an irregular path of an old pipe line and replace the same with new pipes, without correcting the irregular path. Yet another need exists for a lead train that is not rigid, but with components that can move with respect to each other so that it can follow an irregular path.